[英]How to read data from nested array in Firestore
我的 Firestore 中有以下结构,我想读取数据并将其存储在 ArrayList 中,就像我有“amountArrayList”,它将从 Firestore 中的“事务”字段读取数据,我想从“交易”字段并制作它的数组列表,以便我可以以列表方式显示它。
我的代码
Map<String, Object> map = document.getData();
for (Map.Entry<String, Object> entry : map.entrySet()) {
if (entry.getKey().equals("transactions")) {
System.out.println(entry.getValue().toString());
}
}
Output
[{transactionType=Credit, amount=3000, dateToStr=17/12/2021, timeToStr=08:06:10, description=}, {transactionType=Credit, amount=2000, dateToStr=17/12/2021, timeToStr=08 :06:50,描述=}]
由于transactions
是一个数组字段,因此您从entry.getValue()
获得的值是一个对象List
。 由于 JSON 中的每个对象都具有属性,因此在 Java 代码中,它们每个都将再次成为Map<String, Object>
。
打印金额的简单方法如下:
List transactions = document.get("transactions");
for (Object transaction: transactions) {
Map values = (Map)transaction;
System.out.println(values.get("amount")
}
虽然 Frank van Puffelen 的回答可以很好地工作,但有一个解决方案,您可以直接将“事务”数组 map 放入自定义对象列表中。 假设您有一个如下所示的 class 声明:
class User {
public String balance, email, firstname, lastname, password, username;
public List<Transaction> transactions;
public User(String balance, String email, String firstname, String lastname, String password, String username, List<Transaction> transactions) {
this.balance = balance;
this.email = email;
this.firstname = firstname;
this.lastname = lastname;
this.password = password;
this.username = username;
this.transactions = transactions;
}
}
一个看起来像这样的:
class Transaction {
public String amount, dateToStr, description, timeToStr, transactionType;
public Transaction(String amount, String dateToStr, String description, String timeToStr, String transactionType) {
this.amount = amount;
this.dateToStr = dateToStr;
this.description = description;
this.timeToStr = timeToStr;
this.transactionType = transactionType;
}
}
要获取列表,它将非常简单:
docRef.get().addOnCompleteListener(task -> {
if (task.isSuccessful()) {
DocumentSnapshot document = task.getResult();
if (document.exists()) {
List<Transaction> transactions = document.toObject(User.class).transactions;
List<String> amountArrayList = new ArrayList<>();
for(Transaction transaction : transactions) {
String amount = transaction.amount;
amountArrayList.add(amount);
}
// Do what you need to do with your amountArrayList
}
}
});
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